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FLEXO Magazine : November 2010
Technologies & Techniques Right Tape/Right Plate: How Do I Tell? Cushion Mounting Tape Battles Banding in Print By Brett Kilhenny Itis important to remember when selecting a plate and cushion mounting tape, that they act as a single unit when on press and their interaction needs to be understood to optimize print quality. In large part, the type of ink, substrate, and print quality requirements of the job determine selection of the plate. The old rule of thumb for choosing a cushion tape was that process work benefits from softer or lower com- pressibility tapes, while line and solid work is best done with firmer or higher compressibility tapes. However, the recent introduction of digital plates and the high-speed capabilities of modern presses can make tape selection more difficult. Today ’s printing challenges require consideration of both compressibility and the dynamic response of plate and tape acting as a single unit. To demonstrate this point, a print study was completed using different durometer plates in combina- tion with tapes of varying compressibility and composition (i.e. open cell urethane versus closed cell polyolefin). The resiliency of the tapes and plates was also measured. This revealed whether the material was energy absorbing (damping) or resilient (springy). A good way to visualize this is to picture dropping a steel ball bearing on the plate and tape and observing how high it bounces. If the ball bounces back to almost its original drop height, it is very resilient. If it bounces back only a small portion of the original drop height, it is energy absorbing or a damping material. The effects on gear band reduction, dot gain, and solid ink density were measured and compared with the physical properties to determine if trends in print performance could be better predicted when both compressibility and resiliency were considered. Gear banding was measured using a pre-determined grid of solid ink density measurements with the standard devia- tion of the readings being reflective of the degree of band- ing. What was found is that a soft, energy absorbing plate and tape combination is better at minimizing gear banding. Increasing the firmness and resilience of the combination resulted in the higher incidence of banding. It is important to remember that there is no magic bullet to completely elimi- nate gear banding in all situations but softer, more energy absorbing plates and tapes help. The same was found to be true for reducing dot gain. Softer, more energy absorbing tape and plate combinations minimized dot gain while the firmer and more resilient combinations in- creased dot gain. The solid ink density response was a bit more complicated. Combinations of plate and tape that were both soft and highly resilient had the lowest solid ink density. Soft and energy absorbing combinations provided improved solid ink density, but medium and firm compressibility combinations that were energy absorbing provided the highest SID. One notable exception to the above observations was that digital plates provided very low dot gain in combination with firmer energy absorbing tapes. In general, the open cell ure- thane foam technology used in some commercially available cushion mounting tapes provides energy absorbing perfor- mance that is advantageous to improved print performance with today ’s digital plates and high press speeds. n ABOUT THE AUHOR: Brett Kilhenny is new business develop- ment manager for Rogers Corp. The cushion mounting tapes and plates used in the print study to evaluate the effect of compressibility and resiliency on print quality. (PuR means open cell urethane and Po means closed cell polyolefin.) All are courtesy Rogers Corp. This plot shows the compressibility (soft versus firm) and resiliency (energy-absorbing or springy) of the plates and tapes. • No Magic Bullet Eliminates Banding. • Soft, Energy-Absorbing Tapes Can Minimize Banding • Digital Plates, High-Speed Presses Must Factor into Tape Selection Criteria. 50 FLeXO noveMBeR 2010 www.flexography.org Should have used R/bak® Plate Mounting Cushion. He did. Rogers R/bak® open cell urethane technology delivers superior compressibility to reduce dot gain and increase solid ink density. It's the premier cushion mounting tape for consistently higher quality print results at higher speeds over the entire press run with no adjustments. Rogers Corporation High Performance Foams Division 245 Woodstock Road, Woodstock, CT 06281-1815 U.S.A. Phone: 607.786.8112 Fax: 607.786.8120 www.rogerscorp.com/rbak | email@example.com Narrow web press photo courtesy of Rhode Island Label Works, Inc. ROGERS_FLEXO_1210.qxd 10/27/10 10:45 AM Page 1 FLX_Nov10_mech.indd 50 11/1/10 2:25 PM
Sustainable Fall 2010